insulation / screed query on new self build

stef22

Our self-build house is now weather-tight and just had the first fix plumbing done, i now need to put down the insulation before we can pour the screed.

We have hollow-core so screed upstairs as well. Upstairs will have 50mm Kingspan with 75mm screed, downstairs will have 50mm Kingspan + 100mm Kingspan with 50mm screed. It is an airtight house.

I am unsure about 2 things therefore my questions here.

With regards to the 1000g polythene, does it go directly on the slab and then you put the insulation or is it the other way around? My understanding is that you would put first the insulation and then the polythene, this way it will stop the screed from leaking but get contradicting infos. The polythene will have to go on the hollow-core as well then or is it purely on the main slab downstairs to prevent damp?

Second, planning to fit at screed level 25mm insulation on every wall to allow for screed expansion and prevent the heat coming from the underfloor to "go next door", any other tips or tricks i could do ?

Many thanks in advance for your help.

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Tefral

I taped my boards with duct tape and then put the polythene sheet down. That stops the screed from getting below the boards and then lifting them up. I taped it up the walls about 150mm all the way around and then just cut it off.

stef22

Thank you Tefral for taking the time to answer,you didn't put any insulation around to allow for expansion? I see you didn't put the door frames before the screed , I will either put them before or put a bit of insulation before pouring the screed that will allow to fit them in.

Tefral

https://www.boards.ie/discussion/comment/121483582#Comment_121483582

I did. The walls are lined with 62.5mm boards so if you look under where they stop you can see a line all around, thats then where i put in the perimeter insulation

stef22

great thanks Tefral